Curing prolamine fibers with aldehyde in liquid organic medium



Patented Oct. 3, 1950 CURING- PROLAMINE FIBERS WITH" ALDE HYDE IN LIQUID ORGANIC MEDIUM Glarence Bradford Croston, Cyril D. Evans, Leonard L. McKinney, and John C. Cowan, Peoria, Ill;,.assignors to the United States of America as-represented by the Secretary of Agriculture No: Drawing. Application. April 20,1948,

Serial No 22,234

liClaims. (Cl. 8-1216) 7 I (Granted underthe act of March 3, 1883, as amended April 30, 1928;370 0. G. 757

This application is made under the act of March}; 1883', as amended by the actofApril 30, 1928; and the invention herein described, if patented in any country, may be manufactured and. used by or for the Government of the United States of America for governmental purposes throughout the world without the payment to us of any royalty thereon;

This invention relates to' a novel method for treating shaped prolamine bodies to increase water-resistance and reduce shrinkage on exposure'to aqueous environment and is particularly'directed" to a method for curing fibers or filaments'from Zein. This invention contemplates a curing process in anessentially nonaqueous medium.

This invention'hasamong its objects the provision of a process whereby-Zein fibers either uncured'or curedby presentlyknown methods, is given a treatment to produce an acid-stable. water-resistant fiber having strength-properties after an acid' boil heretofore unattainable.

A further object of this invention is the provision of a curing process 'for. such zein fibers that is rapid and economical, and may be effected on the-fibers in the bulk or loose state.

Zein fibers are produced mainly by a wetspinning'process iIl'WhiCh an alkaline dispersion is spun into a coagulating bath, usually acid, and given" subsequent various precuring, stretching, drying and curing treatments. These prior precuring and curing steps involve aqueous aldehyde-treatment of-onetype or another, and result in fibers or filaments having desirable strength and handling propertie when dry. All, however, have undesirable water absorption and shrinkage characteristics which materially reduce the utility of zein fibers in fabrics or other purposes involving exposure to water, alkalis or acids. To our knowledge no cure has heretofore been proposed involving a nonaqueousmedium to produce acid stable cross-linkages.

It has been proposed to prepare zein films from casting solutions comprising limited amounts of water-in which is also present an aldehyde and a small amount of acid catalyst. Such a process is described in U. S. Patent No. 2,402,128 issued toC'yril D. Evans. This process involve preparing the solution in a substantially volatile solvent, casting the film and subsequently baking at 130 C. Thebaking'treatment is required to achieve non-blushing products.

It has also been proposed to impart waterresistance and decreased shrinkage characteristics to zein fibers by baking acid-aldehyde-cured zein fibers at relatively high temperatures to impart desired water resistance and low shrinkage. Furthermore the proposal has been made to produce zein film forming dispersions stable against gelation involving heat treating an aqueous -al-- to improve its water-resistance zein fibers haveformerly been given an aqueous aldehyde cure. The curing is usually done at elevated tempera'-' tures to promote rapid reaction. Tension on the fiber is required to prevent shrinkage and weakening. The resulting fiber is brittle, and the filaments become plastered'together in the presence" of'water. It is not water-resistant to any satisfactory degree. This cure is carried out in a relatively high concentration of mineral acid in order to produce stable aldehyde'linkages, but the acid environment is injurious to the fiber; Inorder to reduce the aforementioned difiiculties it has been subsequently found desirable to supplementthe aqueousaldehyde cure" by a dimcult and expensive acetylation, usually prior'to the final aldehyde cure; These acetylated fibers are also considerably benefited by our process.

The'objects of thi invention are accomplished. byan acid-catalyzed aldehyde'cure carried out atelevated' temperatures in a substantially anhydrous medium. The curing is effected by an aldehyde or aldehyde yielding. agent. The third component of the curing medium is an insert organic liquid which serves as a=solvent (or chemi-' cal contact" promoter) for the aldehyde, and fiber.

The process of this invention, when used to cure fibers or filaments, may becarried out either on the bulk or loose material, or the material may be held under tension in the curing medium.

Our invention is particularly adaptable to fibers, and we prefer to use precured fiber which" has been stretched and dried as described'in U. S. Patent application 3. N. 528,479, filed March 28, 1944. However, Zein fibers regardless of mode of spinning or subsequent treatment or modification are benefited by our curing method. In fact,"

any fiber or other shaped body essentially prolamine which exhibits shrinkage or high Water invention.

The inertliquids used accordingto our invention may vary widely. We have found that par affinic or aromatic hydrocarbons yield excellent results. Also, oxygenated organic solvents that absorption can be treated to advantage b our are inert to the aldehyde and prolamine have Examples of likewise given excellent results. suitable solvents are benzene, toluene, xylene, petroleum ether, Stoddards' Solvent, butanol,

cyclohexanol, dioxane, nitrobenzene, and the like: Theifunction i of the inert liquid :is to serve'as a chemical contact medium between the aldehyde and the fiber, and to effect catalytic contact with the acid. The term inert is intended to refer to the absence of chemical reaction which destroys the prolamine, acid or aldehyde. Complexes such as occur between such liquids as dioxane and the acids do not materially affect the process.

Although we term our medium "essentially non-- aqueous, the process is not limited to absolutely anhydrous conditions. For example, results are obtained using media containing as much as 2 percent moisture. This fact is important when using ,solvents such as dioxane which tolerate and usually contain unavoidable small but appreciable amounts of water. However, more than 2 percent total water begins to cause excessive shrinking of the fiber.

The aldehyde used is preferably formaldehyde because of its reactivity and low cost. aldehydes may be used such as acetaldehyde, glyoxal, propionaldehyde or polymers of these. The aldehyde may be added as such or as aldehyde yielding agents. Examples are Formalin, paraformaldehyde, trioxane, or dioxolane. With the exception of Formalin or other aqueous solutions of aldehyde, the amount of aldehyde compound is not critical. The use of aqueous solution such as Formalin should be carefully controlled because, as previously stated, more than 2 percent total water causes excessive shrinking of the fiber. In general, aldehyde yielding agents are used at higher concentrations than the aldehyde, per se. Their efiectiveness depends mainly upon their rates of decomposition. In all such 1 agents named these rates are adequate. Commercial dioxane contains sufiicient aldehyde yielding impurities to give good results.

The function of the acids used is primarily to catalyze reaction between the aldehyde and the prolamine body. Consequently the amount and kind of acid may vary widely. In general, we have found the class of mineral acids and strong organic acids suitable. Any acid having a dissociation constant greater than K=l.5 gives satisfactory results. Examples are sulfuric, hydrochloric, phosphoric,i trichloroacetic, and d chloroacetic acids. The amount of acid used naturally varies with the kind of acid, but we have found in general that the concentration need not be greater than 5 percent by weight of the curing medium,- and is preferably within the range of 0.1 to 1 percent, Strong organic acids can. be used atmuchhigher concentrations, especially in solvents such as toluene, in which the inorganic acids are rather insoluble;

The temperature of the cure and the time of curing are interrelated and also dependent upon the strength of the acid in the medium. In general, temperatures of 75 C. and above are sufficient. The time varies from 5 minutes to 45 minutes, the shorter time corresponding to the temperature of reflux of the liquid used. At temperatures at or near the boiling point of the curing mixtures, the reaction is very rapid, and is. ordinarily complete within minutes. In general, the temperature should not be over 150 C., but with the solvents named, the reflux temperature is below this. However, other higher .boiling liquids may be used, provided the maximum temperature of cure is kept below 150 C.

The rate of the reaction can be established by reference to the percent shrinkage in boiling acetic acid of the cured fiber. When zein fiber was treated with dioxane, 2000 parts; Formalin,

Other assainaa 32 parts; and sulfuric acid, 1 part; the percent shrinkage, so determined, dropped sharply in the range 2 to 5 minutes, continued to drop in the range 5 to 15 minutes, and remained substantially constant after 15 minutes of treatment.

When zein fiber was treated for 15 minutes in milliliters of dioxane, 0.1 milliliter of Formalin, and 0.025 milliliter of sulfuric acid at temperatures ranging from 40 C. to 104 C., the percent shrinkage of the cured fiber (determined by and brought about by boiling in acetic acid) dropped continuously in a steep curve from about at 40 C. to about 6% at 104 C. The percent shrinkage caused by the curing solution remained substantially constant at about 5% to 9% in the range 40 C. to 104 C.

The desired reduction in total shrinkage may be accomplished in shorter time by increasing the temperature.

The specific reaction of this invention, 1. e., the type and manner of linkage formed is not known precisely. It is believed that the crosslinkages are formed between active groups of the protein molecules in order to give the dimensional stability characteristic of fiber produced according to our invention. We do know, however. that the linkages are not the usual type of linkages encountered by conventional curing methods carried out in the presence of an appreciable amount of water. The linkages in these prior cured fibers are readily reversibly hydrolyzed by hot dilute acids. According to the invention the aldehyde is irreversibly bound. The aldehyde content cannot be determined by the usual hydrolytic methods for determining reversibly bound aldehydes.

After the treatment, the fiber should be washed and dried. The wash may be eifected by either an organic solvent or water. Itis desirable to include a base such as pyridine or a carbonate to facilitate removal of residual acid from the curing bath.

Being nonaqueous, the cure has several advantages over aqueous cures of the prior art. The fiber can be cured while loose without causing excessive shrinkage thus eliminating equipment necessary to cure under tension. The highest temperatures concomitant with the particular inert liquid used make possible a rapid cure without serious damage to the fiber. The productis stable to acid as well as alkaline hydrolysis. According to our process, fibers are produced having practically no shrinkage in boiling acid baths and have strengths, after acid boil, of 1.4 g. per denier, dry and 0.7 g. per denier, wet. These strengths are equal or superior to those of a good grade of wool after an acid boil.

Precured zein fibers (stretched and dried after a weak preliminary cure in aqueous formaldehyde) shrink about 70 percent of their length in boiling water, are practically solubilized in boiling dilute acetic acid, and dry to a horny mass. These same fibers after being treated according to the present invention while held at constant length shrink less than 10 percent in boiling dilute acid and after drying are still very strong and firm and have a good hand If the fibers are cured by the present invention while loose in mixtures such as No. 1 or 2 of the following examples, part of the shrinkage occurs during the treatment so that the resulting fiber is strong and has a very low shrinkage. When the treated fiber is washed by relaxing in a warm aqueous alkaline solution prior to drying, it has no shrinkage even in boiling dilute acid.

smears 'ifhefollowingexamplesillustratetheinvention; but :are not; to beeconsideredas limiting. The parts given: are by weight unless .otherwisegstat'ed:

EXAMPLE 1v Zeincfibers were: treated for '15,, m nutes .1 a refluxing mixture, of th following composition:

5. v parts dioxane (para) 4 parts .Formalin 2Iparts sulfuric acid 7 EXAMPLE 2;

The procedure of Example 1 was repeated, em-

ploying a refluxing mixture of; they following composition:

500 parts toluene" Smpa-rts: paraformaldehyde 2 parts hydrogen chloride EXAMPLE 3 The-procedure of Example 1 was repeated, em-

ploying-a,- re-fluxingmixture of the following composition:

4001parts dioxane (para) 100 parts 4-methy1 di'oxolane parts hydrogen chloridev The procedure of Example 1 was repeated, employing a, refluxing mixture of the following composition:

500 parts dioxane (para) 3 parts glyoxal (40 percent aqueous solution) 1 part sulfuric acid EXAMPLE 5 The procedure of Example 1 was repeated, employing a refluxing mixture of the following composition:

500 parts toluene 50 parts trioxane 8 parts hydrogen chloride EXAMPLE 6 The procedure of Example 1 was repeated, employing a, refluxing mixture of the following composition:

500 parts toluene 50 parts paraformaldehyde 5 parts dichloroacetic acid EXAMPLE 7 Zein fibers were treated for minutes at 110 C. in a mixture of the following composition:

500 parts Stoddards Solvent 10 parts paraformaldehyde 5 parts trichloroacetic acid The treatment was carried out on the bulk fibers. After treatment, the fibers were washed in acetone.

EXAMPLE 8 The procedure of Example 1 was repeated using the same curing medium. The fibers, before treatment, had been subjected to a stretching treatment.

Th'eprocedureof Example ,1 was repeated; using thesame curingmediumjexcept that the fibers were. cullednwhil'e under tension and had been iven a stretchingtreatment before the cure.

' The-fibers cured in accordance withthe above examples, had? the; following shrinkage, and st e ths.

Table,

Shrink? Strengths after age (per boiling in cent) dilute acetic upon acidforlfi ExampleNo: boiling minutes indilute (Grams per acetic denier) I acid for 1.5. 7 minutes Dry Wet Theifibersused in the above examples were produced by a wet spinning 'process in accordancewith the procedure of the Evans. disclosure notedv previously. Zein fibers produced by other methods may be substituted'such as raw, precured'; or acetylated. The results are. substan-. tially thesame.

Our curing processis applicable to other substantially prolamineshapedibodies such as films, ribbons, bristles; or molded bodies, to improve water resistance and reduce shrinkage.

Stoddards Solvent, employed in Example 7 is a Well-known petroleum hydrocarbon dry cleaning solvent. Its specifications are set forth in the Bureau of Standards Bulletin 083-28.

The drying step employed in the above examples was carried out at atmospheric conditions. Other drying methods may be employed as for example at slightly elevated temperatures. The drying conditions are not critical in the process according to our invention.

Having thus described our invention, we claim:

1. A method which comprises treatin a prolamine shaped body with a member of the group consisting of aldehydes and aldehyde yielding compounds in an inert liquid organic medium, in the presence of an acid'having a dissociation constant not less than K =1.5 10- the acid being present in a quantity not more than 5 percent by weight of the aldehyde and the inert liquid organic medium, the total water content ranging from zero to not more than 2% by Weight, the treatment being at 75-l50 C., washing the shaped body, and drying it.

2. The method of claim 1 in which the prolamine shaped body is zein fiber.

3. The method of claim 1 in which the prolamine shaped body is zein fiber and the treatment is under inert liquid organic medium reflux and at atmospheric pressure.

4. The method of claim 1 in which the prolamine shaped body is zein fiber, the treatment is under inert liquid organic medium reflux, and the organic medium is one having a boiling point not lower than C.

5. A method which comprises curing zein fibers by treating said fiber with a member of the group consisting of an aldehyde and aldehyde yielding compounds in an inert and substantially nonaqueous liquid organic medium, in the presence of a catalytic amount of an acid having a. dissociation constant not less than K=1.5 10 there being present not more than 2 percent of water, said treatment being carried out at a temperature within the range of 75-150 C. and said amount of acid being not greater than percent by weight of the curing medium.

6. Process of claim 5 in which the inert organic liquid is dioxane.

7. Process of claim 5 in which the inert organic liquid is toluene.

8. Process of claim 5 in which the inert organic liquid is Stoddards Solvent.

9. Process of claim 5* in which the acid use is hydrogen chloride.

10. Process of claim 5 in which the acid used is sulfuric. V

11. Process of claim 5 in which the acid used is trichloroacetic.

12. A method of curing zein fibers comprising treatin said fiber with a member of the group consisting of aldehydes and aldehyde yielding compounds in dioxane in the presence of hydrogen chloride, the hydrogen chloride being present in a quantity not more more than 5- percent by weight of the aldehyde and solvent, the total water content ranging from zero to not more than 2 percent by weight, at a temperature between 75-150 C.

13. The process of claim 12 in which the treatment is under dioxane reflux and the aldehyde is formaldehyde.

14. A substantially non-aqueous curing process for making strong zein fibers having a low shrinkage in which the aldehyde is substantially irreversibly bound and cannot be determined by the usual hydrolytic methods for determinin reversibly bound aldehydes, comprising treating zein fibers with formaldehyde in an inert liquid organic medium, in the presence of an acid having a dissociation constant not less than REFERENCES CITED The following references are of record in the fiie of this patent:

UNITED STATES PATENTS Number Name Date 1,210,394 Anders Jan. 2, 1917 1,395,191 Lambeck Oct. 25, 1921 2,322,486 Swallen et a1. June 22, 1943 2,359,202 Coleman Sept. 26, 1944 FOREIGN PATENTS Number Country Date 573,432 Great Britain Nov. 21, 1945 

1. A METHOD WHICH COMPRISES TREATING A PROLAMINE SHAPED BODY WITH A MEMBER OF THE GROUP CONSISTING OF ALDEHYDES AND ALDEHYDE YIELDING COMPOUNDS IN AN INERT LIQUID ORGANIC MEDIUM, IN THE PRESENCE OF AN ACID HAVING A DISSOCIATION CONSTANT NOT LESS THAN K=1.5X10**-3, THE ACID BEING PRESENT IN A QUANTITY NOT MORE THAN 5 PERCENT BY WEIGHT OF THE ALDEHYDE AND THE INERT LIQUID ORGANIC MEDIUM, THE TOTAL WATER CONTENT RANGING FROM ZERO TO NOT MORE THAN 2% BY WEIGHT, THE TREATMENT BEING AT 75*-150*C., WASHING THE SHAPED BODY, AND DRYING IT. 